The present invention relates generally to devices for providing an indication of an undesirable engine condition, and more particularly, to an overload warning apparatus for an engine.
Various apparatus are known in the art to indicate the engine speed of an internal combustion engine. These apparatus are generally designed to indicate when a maximum engine operating speed is exceeded by use of a visual or audio indicating device and may further operate to decrease the engine operating speed below the predetermined maximum speed.
U.S. Pat. No. 3,794,971 discloses a vehicle speed sensing device in which an alarm signal is activated when the speed of the engine exceeds a predetermined value. As the rotational speed of the shaft within the governor assembly increases, flyweights are caused to pivot outwardly and thereby move a sleeve member axially along the rotating shaft. The sleeve member in turn pivots a fork-shaped member having a pair of annular permanent magnets disposed therein and thereby urges the annular magnets into close proximity to a switching device having a reed switch therein. The switching device is connected via an electrical connection to an alarm which indicates that the vehicle's speed is approaching an upper speed limit. Thus, this patent provides an audio indication to a user who can then adjust the speed of the vehicle accordingly.
U.S. Pat. No. 2,983,911 also relates to an engine speed warning system for an internal combustion engine. When the engine speed reaches a predetermined level, a vacuum is created to activate a maximum speed governor. The maximum speed governor slows the engine speed by closing the engine throttle and further functions to operate a visual or audio warning indicator. Thus, this patent not only provides an indication of excess speed to a user, but also operates to decrease the engine operating speed below a predetermined maximum speed.
An engine overload condition differs from an excess engine speed condition in that the engine operating speed is too slow relative to the load being placed on the engine. For example, in an internal combustion engine used on a lawn mower, the ground speed of the mower may be too high relative to the power output from the mower. If tall grass is encountered during mowing, or a steep grade is encountered during transportation, the mower engine may be "lugged down" because the power output of the mower is insufficient under the operating conditions. Thus, in contrast with an excess engine speed condition, the speed of an internal combustion engine must be increased during an engine overload.
U.S. Pat. No. 3,281,783 generally discloses an engine overload indicator having a diaphragm responsive to engine vacuum pressure which operates a switch. The switch in turn operates a flasher and an audio alarm to alert an operator that an overload condition exists. The operator can then take corrective measures to increase the engine speed to an acceptable level by reducing the load on the engine, e.g., reducing the ground speed of the vehicle.
It is desired to provide an engine overload indicator that is compact and reliable for use in small internal combustion engines.